1. Field of the Invention
The present invention, in general, relates to drawbars for towing a trailer and, more particularly, to a drawbar that will dampen the forces of shock and impact that occur between a towing vehicle and a trailer being towed.
A trailer, like all objects, has inertia. When it is at rest, it tends to remain at rest unless acted upon by some force to the contrary. Similarly a trailer in motion tends to remain in motion unless also acted upon by a force to the contrary.
A contrary force is provided by irregularities in a road surface, by gravity and by the towing vehicle when either accelerating or braking. The trailer and towing vehicle are connected together by any of a variety of hitch arrangements; a ball type of hitch coupling arrangement being the most common, and a pintle type of hitch coupling is used sometimes for towing heavier trailers.
Any hitch coupling is a mechanical device having mechanical tolerances between its component parts. These tolerances produce a cumulative gap between the component parts that is more commonly referred to as "slack".
The slack between the component parts of a trailer hitch produces a shock impulse when accelerating as a result of having the towing vehicle move slightly forward before the trailer begins to move. As such, a shock impulse occurs momentarily when all of the existing slack has been taken up by the forward motion of the towing vehicle, and a sudden transference of kinetic energy occurs at the towing interface in the form of an impact.
Similarly when decelerating, either the towing vehicle or the trailer will begin to slow first, depending upon whether trailer brakes are used and how they are adjusted, and once again, when all of the slack has been taken up, an impact will occur.
The impact is perceived by occupants of the towing vehicle as a jolt. The severity of the jolt is proportional to the differences in inertia that arise between the towing vehicle and the trailer. A jolt will occur whenever an imbalance occurs between the inertia of the trailer and the inertia of the towing vehicle.
The severity of the jolt is representative of the balancing of kinetic energy between the towing vehicle and the trailer. Jolts of varying severity occur during acceleration, deceleration and also during normal transit as slight differences in velocity between the towing vehicle and the trailer develop.
Since it is not a practical option to eliminate all slack by reducing the sum total of all of the mechanical tolerances of a trailer hitch and coupling to zero, arrangements that will absorb and dampen shock impulses are preferred.
Such structures, in general, utilize dampening techniques. Mechanical trailer hitch dampening techniques will smoothly and temporarily absorb some of the kinetic energy, and then, smoothly return that energy back to the towing vehicle and to the trailer, thereby lessening the perception of a jolt having occurred by towing vehicle occupants.
Prior trailer hitch dampening arrangements, that smooth the transfer of energy between a trailer and towing vehicle, tend to be somewhat complex in construction and, accordingly, are expensive. Prior dampening arrangements are not readily adaptable to accommodate trailers of varying weight, nor are they readily adaptable for use with common types of trailer hitches, such as for use with receiver types of hitches where a variety of drawbars are inserted.
Accordingly, there exists today a need for an energy dampening drawbar capable of dampening the shock impulses that arise between a trailer and a towing vehicle that is adaptable for use with standard types of receiver hitches and is also adaptable for use with specialty types of receiver hitches including wide ranging types of hitches, ball hitches, and pintle hitches.
2. Description of Prior Art
Energy dampening hitch systems, in general, are known. For example, U.S. Pat. No. 4,515,387 to Schuck that issued May 7, 1985, describes a hitch with a swiveling tongue having cushions to absorb the shock loading.
While the structural arrangements of various types of drawbar devices, at first appearance, have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.